I don't recognize them but I can offer you this: They are formed by seaweed being ripped from the bottom of the sea shortly from the edge of the sea. In a location where the movement of the waves is moving in. In all likelihood they are made up of multiple different types of seaweed. One possible type that could be in that mess is:
I would recommend that if possible. Get a sample of the seaweed. Take it to a lab and stick it under a fairly high powered microscope. See what it looks like because that will help you. If you can get a picture of the microscopic view to show us. Here is a site that might help you.